The present invention relates generally to operations performed in conjunction with a subterranean well and, in an embodiment described herein, more particularly provides a wellbore junction isolation method and associated apparatus.
Wellbore junctions are formed at intersections of wellbores in a well. For example, a main or parent wellbore may have a branch or lateral wellbore drilled extending outwardly from an intersection between the main and branch wellbores. Of course, the main wellbore may extend below the intersection with the branch wellbore, for example, to intersect a formation from which it is desired to produce hydrocarbons into the main wellbore.
Unfortunately, however, some wellbore junctions are not able to withstand substantial internal pressure applied thereto. For this reason, pressure within these wellbore junctions is limited to the fracture gradients of the respective formations in which the wellbore junctions are positioned. Thus, if stimulation operations, such as fracturing, must be performed for any formations below the wellbore junctions, expensive, time-consuming and/or complicated procedures must be used to prevent exceeding the fracture gradients of the formations at the wellbore junctions. Similar problems may also arise in other, non-stimulation types of well treatment such as, for example, circulation, washing and cleaning operations.
Therefore it would be quite desirable to provide a method of isolating a wellbore junction which is convenient and easily performed, and which isolates the wellbore junction from pressures applied through the junction.
In carrying out the principles of the present invention, in accordance with an embodiment thereof, a method of isolating a wellbore junction is provided in which an isolating assembly is positioned at the wellbore junction and sealingly engaged with spaced apart wellbore portions. The assembly isolates at least one flow passage extending therethrough from the wellbore junction. Pressure may then be applied to the flow passage without that pressure being communicated to the wellbore junction.
The isolating assembly may be operatively positioned in different orientations to protectively isolate the junction from fluid pressure being exerted within either selected one of two intersecting wellbores such as a main wellbore and an intersecting branch wellbore.
In one aspect of the invention, the assembly includes two sealing devices which are sealingly engaged between the assembly and wellbore portions intersecting at the wellbore junction. The sealing devices are sealingly engaged straddling the wellbore junction. In this manner, an annulus formed between the assembly and the wellbore portions with which the sealing devices are sealingly engaged is divided into three portions, a middle one of which is in fluid communication with the wellbore junction.
In another aspect of the invention, the other two annulus portions are in fluid communication with each other via another flow passage formed through the assembly. Thus, a circulation flowpath is formed between the annulus portions above and below the wellbore junction extending through the assembly.
Preferably, the sealing structures are cup packers which permit the assembly to move longitudinally relative to the wellbore portions with which the assembly is sealingly engaged. This is particularly beneficial in subsea well applications in that the permitted assembly movement relative to the wellbore structure provides automatic compensation for rig heave. A variety of other types of sealing or slip joint structures which permit this compensation could alternatively be utilized if desired.
In yet another aspect of the invention, the assembly is conveniently installed in a single trip into the well and may be positioned entirely within a main wellbore portion or operatively extended from the main wellbore into an associated intersecting branch wellbore portion. A particular embodiment described herein includes inner and outer tubular structures, with the sealing devices on the outer structure, and the inner structure sealed to the outer structure above and below the sealing devices.
These and other features, advantages, benefits and objects of the present invention will become apparent to one of ordinary skill in the art upon careful consideration of the detailed description of a representative embodiment of the invention hereinbelow and the accompanying drawings.